High-strength and high-toughness aluminum alloy material for bumper beam and method for manufacturing the same

ABSTRACT

The present invention discloses a high strength and high toughness aluminum alloy for a bumper beam and a method for manufacturing the same. The method includes: casting into a billet an aluminum alloy which comprises aluminum as a principal element, silicon (Si) of 0.1 wt. % or less, ferrum (Fe) of 0.2 wt. % or less, copper of 0.45 wt. % to 0.60 wt. %, manganese (Mn) of 0.1 wt. % to 0.20 wt. %, magnesium (Mg) of 1.3 wt. % to 1.5 wt. %, chromium (Cr) of 0.1 wt. % or less, zinc of 4.5 wt. % to 5.1 wt. %, titanium (Ti) of 0.04 wt. % or less, zirconium (Zr) of 0.08 wt. % to 0.12 wt. %, and inevitable impurities of 0.15 wt. % or less; extruding the billet into a predetermined form to form an extrusion; performing a solid-solutionization process to quench the extrusion; subjecting the extrusion to an artificial age-hardening which is performed at a temperature of about 120° C. for 24 hours; and subjecting the extrusion an over age-hardening which is performed at a temperature of about 170° C. to 185° C. for 1 hour to 3 hours.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(a) on Korean Patent Application No. 10-2007-0057548 filed on Jun. 13, 2007, the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a high strength and high toughness aluminum alloy suitable for a bumper beam of a vehicle and a method of manufacturing the same.

2. Background Art

Researches on lightweight materials for reducing the weight of a transportation machine such as a vehicle or an aircraft have been undergone for years, and an aluminum alloy has been the most popular material satisfying such a need.

Since an aluminum alloy has high strength and light weight, it is extensively used as a material for a vehicle, an aircraft, etc. or as a material for construction industry.

An aluminum alloy is currently being used in various industrial fields, for example, as electrical and electronic parts of telecommunication equipments, semiconductor devices and computers, leisure supplies, and small-sized products such as components of a vehicle.

An aluminum alloy is grouped into a casting aluminum alloy and a wrought aluminum alloy. The wrought aluminum alloy is further divided into: (i) a high-strength aluminum alloy such as a duralumin based alloy, an Al—Cu—Mg based alloy, and an Al—Zn—Mg based alloy; and (ii) a corrosion-resistant aluminum alloy such as an Al—Mn based alloy and an Al—Mg—Si based alloy.

An aluminum alloy is identified by four digits which are prescribed by Aluminum Association. 1000 to 8000 series are used, in which 2000 and 7000 series denote a high-strength aluminum alloy.

Recently, researches on the 7000 series alloy which has the highest strength are actively being undergone. Since the 7000 series alloy is an Al—Zn—Mg based alloy containing MgZn2, its age-hardening property is notable.

Representative 7000 series alloys are Al7003 and Al7021. Such alloys are precipitation hardening alloys which can have a high-strength property when heat treatment is additionally performed after an extrusion process and are also heat-treatable alloys which necessarily require heat treatment to cause the strengthening effect by forming eduction through magnesium (Mg) and zinc (Zn).

The heat treatment can be varied depending on the kind of the aluminum alloy. T6 heat treatment is usually used for the 7000 series alloy. The T6 heat treatment is performed such that an alloy is heated at a temperature of 400° C. to 500° C. to be solid-solutionized and then rapidly cooled in water. The cooled alloy is heated at a temperature of about 120° C. for 24 hours to be artificially age-hardened.

Here, the age-hardening is a phenomenon that a metal material gets hardened when it is disposed at a predetermined temperature for a predetermined time. The age-hardening can be made by naturally or artificially. That is, a metal material can be hardened at a room temperature, or it can be hardened with heat treatment.

One mechanism of the age hardening is a precipitation phenomenon that a solid exists with another solid in different phases.

The strength of the 7000 series aluminum alloy is increased by increasing the contents of magnesium (Mg) and zinc (Zn) and performing the artificial age-hardening so that MgZn2 can be precipitated. In this instance, however, its resistance to intergranular brittleness and intergranular stress corrosion gets lowered.

In the 7000 series aluminum alloy, an atomic ratio of Zn/Mg is about 2 to 2.5, and the zinc (Zn) content is set to 3 wt. % to 7.5 wt. % and the magnesium (Mg) content is set to a level that can lead to quantitative reaction of MgZn2. It is why there is little difference between magnesium (Mg) and zinc (Zn) in solid-solution strengthening effect, and in an alloy that magnesium (Mg) is excessively contained, Al3Mg2 which may be produced according to a heat treatment condition is very harmful to stress corrosion.

As described, aluminum is being used in various alloy forms. Particularly, in the 7000 series aluminum alloy, a high strength property is achieved by adding magnesium (Mg) and zinc (Zn) as principal elements and the other transition elements as secondary elements. Such a high-strength aluminum alloy, instead of a heavy steel material, is used to manufacture various parts which require a high strength property.

A process for manufacturing a certain product by using the 7000 series aluminum alloy is as follows. An aluminum alloy in which various transition elements are contained with a composition ratio which satisfies a desired characteristic is cast into a billet. The billet is extruded in a desired product form to form a product extrusion. The product extrusion is then subject to the T6 heat treatment (i.e., solid solutionization) before hardened by the artificial age-hardening, whereby a high-strength product is manufactured.

However, the high-strength aluminum alloy material of 7000 series still has a problem in that while its elongation is high, its toughness is so low as not to be sufficiently transformed by a crash, which makes the alloy material not suitable for an aluminum bumper beam of a vehicle.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to solve the aforementioned problems associated with prior arts.

The present invention provides a high-strength and high-toughness aluminum alloy, which is Al—Zn—Mg based alloy, comprising manganese (Mn), copper (Cu) and zirconium (Zr) as additive elements. The composition ratio of the components is adjusted in a predetermined range. In order to manufacture a high-strength and high-toughness aluminum alloy material, the aluminum alloy with a predetermined composition ratio is first cast into a billet. The billet is extruded to mold an aluminum extrusion. A solid solutionization process is performed to quench the aluminum extrusion in order to completely solid-solutionize alloy elements. The aluminum extrusion is then sequentially subjected to an artificial age-hardening process which is performed at a temperature of 120° C. for 24 hours and an over age-hardening process (i.e., T7 heat treatment) which is performed at a temperature of about 170° C. to 185° C. for 1 hour to 3 hours. Therefore, a high-strength and high-toughness aluminum alloy material is manufactured.

One aspect of the present invention provides a aluminum alloy material with high-strength and high-toughness, comprising: aluminum as a principal element, silicon (Si) of 0.1 wt. % or less, ferrum (Fe) of 0.2 wt. % or less, copper of 0.45 wt. % to 0.60 wt. %, manganese (Mn) of 0.1 wt. % to 0.20 wt. %, magnesium (Mg) of 1.3 wt. % to 1.5 wt. %, chromium (Cr) of 0.1 wt. % or less, zinc of 4.5 wt. % to 5.1 wt. %, titanium (Ti) of 0.04 wt. % or less, zirconium (Zr) of 0.08 wt. % to 0.12 wt. %, and inevitable impurities of 0.15 wt. % or less.

Another aspect of the present invention provides a method for manufacturing an aluminum alloy material for a bumper beam, the method comprising: casting an aluminum alloy into a billet, the aluminum alloy including aluminum as a principal element, silicon (Si) of 0.1 wt. % or less, ferrum (Fe) of 0.2 wt. % or less, copper of 0.45 wt. % to 0.60 wt. %, manganese (Mn) of 0.1 wt. % to 0.20 wt. %, magnesium (Mg) of 1.3 wt. % to 1.5 wt. %, chromium (Cr) of 0.1 wt. % or less, zinc of 4.5 wt. % to 5.1 wt. %, titanium (Ti) of 0.04 wt. % or less, zirconium (Zr) of 0.08 wt. % to 0.12 wt. %, and inevitable impurities of 0.15 wt. % or less; extruding the billet into a predetermined form to form an extrusion; performing a solid solutionization process to quench the extrusion; subjecting the extrusion to an artificial age-hardening which is performed at a temperature of about 120° C. for 24 hours; and subjecting the extrusion an over age-hardening which is performed at a temperature of about 170° C. to 185° C. for 1 hour to 3 hours.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will be described in reference to certain exemplary embodiments thereof with reference to the attached drawings in which:

FIG. 1 is a photograph illustrating a bumper beam made of a high-strength and high-toughness aluminum alloy material according to an exemplary embodiment, where the bumper beam is not destroyed but transformed; and

FIG. 2 is a photograph illustrating a bumper beam manufactured by a conventional aluminum alloy material, where the bumper beam is destroyed.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.

As well known, in the 7000 series aluminum alloy, an Al7021 alloy includes manganese (Mn) 0.1 wt. % or less, magnesium (Mg) of 1.2 wt % to 1.8 wt. % and zinc (Zn) of 5 wt. % to 6 wt. %. As Aluminum Association reported, it has the tensile strength of about 420 MPa and elongation of about 13%.

Therefore, even though the Al7021-T6 alloy has the high tensile strength, it may be easily destroyed due to low elongation and a low impact value, so that it is not suitable for a vehicle bumper beam.

An aluminum alloy for a bumper beam according to a preferred embodiment of the present invention has high toughness and high impact resistance unlike the conventional 7000 series aluminum alloy, e.g., Al7021. To this end, the contents of manganese (Mn), copper (Cu), zinc (Zn), and magnesium (Mg) are adjusted so as to increase toughness, leading to have impact resistance. As shown in Table 1, the aluminum alloy according to a preferred embodiment of the present invention contains aluminum as a principal element, and silicon (Si) of 0.1 wt. % or less, ferrum (Fe) of 0.2 wt. % or less, copper of 0.45 wt. % to 0.60 wt. %, manganese (Mn) of 0.1 wt. % to 0.20 wt. %, magnesium (Mg) of 1.3 wt. % to 1.5 wt. %, chromium (Cr) of 0.1 wt. % or less, zinc of 4.5 wt. % to 5.1 wt. %, titanium (Ti) of 0.04 wt. % or less, zirconium (Zr) of 0.08 wt. % to 0.12 wt. %, and inevitable impurities of 0.15 wt. % or less.

TABLE 1 Composition Ratio (weight %) Si Fe Cu Mn Mg Cr Zn Ti Zr 0.11 0.21 0.45~0.6 0.1~0.2 1.3~1.5 0.11 4.5~5.1 0.041 0.08~0.12

The reason why the aluminum alloy according to a preferred embodiment of the present invention has the above composition ratio is described below in detail.

(1) Manganese (Mn): 0.1 wt. % to 0.20 wt. %

Manganese (Mn) is added to increase elongation when an aluminum alloy is cast into a billet. A transition element Mn materializes particles within an alloy to affect an elongation improvement, but when its ratio is increased, processibility is lowered, so that a mold or a processing machine gets worn and torn. For these reasons, the manganese (Mn) content is restricted to a range that elongation is increased but processibility is not affected, i.e., 0.1 wt. % to 0.20 wt. %.

(2) Magnesium (Mg): 1.3 wt. % to 1.5 wt. %

Magnesium (Mg) is added to increase the alloy strength. If magnesium (Mg) is excessively added, a process hardening phenomenon of an alloy gets hastened, so that processibility is lowered, and extrusion may be impossible according to the size and shape of a product. In order to prevent this, the magnesium (Mg) content is restricted to 1.3 wt. % to 1.5 wt. %.

(3) Zinc (Zn): 4.5 wt. % to 5.1 wt. %

Zinc is also added to increase the alloy strength. It is preferable to add zinc at maximum in order to maximize the alloy strength, but if its content is equal to or more than 6 wt. %, a crack occurs during processing. Such a crack occurs because zinc (Zn) is combined with magnesium (Mg) to form MgZn2, but remaining zinc (Zn) which is not combined with magnesium (Mg) exists in the alloy as an impurity. For these reasons, the zinc (Zn) content is restricted to 4.5 wt. % to 5.1 wt. %.

(4) Copper (Cu): 0.45 wt. % to 0.60 wt. %

Copper (Cu) is added to increase an extrusion pressure. It does not show good stress corrosion cracking property, but a bumper beam is used in the circumstances that are not greatly affected by corrosion. In the present invention, it is important to achieve high elongation and high toughness, and copper (Cu) of 0.45 wt. % to 0.6 wt. % is added.

(5) Zirconium (Zr): 0.08 wt. % to 0.12 wt. %

Zirconium (Zr) is added as an aluminum alloy material according to the present invention. In order to achieve a fine structure and high toughness, zirconium (Zr) of 0.08 wt. % to 0.12 wt. % is added.

A method for manufacturing the aluminum alloy material according to an exemplary embodiment of the present invention is described below in detail.

The aluminum alloy having the above described composition ratio is first cast into a billet by a typical casting method. The billet is extruded in a desired form to mold an aluminum extrusion. The aluminum extrusion is then subjected to a heat treatment process.

The heat treatment method according to the exemplary embodiment of the present invention is performed such that alloy elements are quenched by performing a solid solutionization process in order to completely solid-solutionize alloy elements, is subjected to an artificial age-hardening which is performed at a temperature of about 120° C. for 24 hours, and is additionally subjected to an averaging (i.e., T7 heat treatment) or over age-hardening which is performed at a temperature of about 170° C. to 185° C. for 1 hours to 3 hours.

An experimental example according to the exemplary embodiment of the present invention is described below in comparison with a comparison example. A spirit and scope of the present invention is not limited to the experimental example described below.

EXPERIMENTAL EXAMPLE (“EE”) AND COMPARISON EXAMPLE (“CE”)

Bumper beams of the experimental and comparison examples are manufactured such that aluminum alloys having the below composition ratios of Table 2 are cast into billets by a typical casting method, the billets are extruded to form a bumper beam extrusion. The bumper beam extrusions are then subjected to the T6 heat treatment and then subjected to an over age-hardening which is performed at a temperature of 180° C. for one hour. Here, Comparison Example represents the Al7021 alloy.

TABLE 2 Composition Ratio (weight %) Si Fe Cu Mn Mg Cr Zn Ti Zr EE 0.046 0.078 0.664 0.147 1.356 0.001 4.89 0.034 0.115 CE 0.081 0.132 0.113 0.095 1.250 0.098 5.75 0.024

Tensile strength, yield strength, elongation, impact energy of the bumper beams manufactured according to the experimental and comparison examples are measured, and the measurement result is shown in Table 3.

TABLE 3 Tensile Strength Yield Strength Impact Energy (MPa) (MPa) Elongation (%) (Kgm/cm²) EE 404.4 371.2 15.6 8.4 CE 401.2 374.2 16.0 2.0

As can be seen in Table 3, the aluminum alloy bumper beam manufactured by additionally performing the overaging heat treatment process according to the present invention have four times improved impact energy (toughness) in comparison with the conventional aluminum alloy bumper beam even though strength and elongation are similar.

As described above, the high-strength and high-toughness aluminum alloy according to preferred embodiments of the present invention has manganese (Mn), copper (Cu) and zirconium (Zr) as principal elements, but unlike the 7000 series aluminum alloy, e.g., Al7021, the contents of manganese (Mn), copper (Cu), zinc (Zn), and magnesium (Mg) are adjusted to increase toughness and have high impact resistance. The aluminum alloy with such a composition is cast into a billet, the billet is quenched through the solid solutionization process and is extruded into a bumper beam extrusion, and the bumper beam extrusion is sequentially subjected to the artificial age-hardening and over age-hardening, thereby providing the high-strength and high-toughness bumper beam.

Although the present invention has been described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that a variety of modifications and variations may be made to the present invention without departing from the spirit or scope of the present invention defined in the appended claims, and their equivalents. 

1. An aluminum alloy material with high-strength and high-toughness, comprising: aluminum as a principal element, silicon (Si) of 0.1 wt. % or less, ferrum (Fe) of 0.2 wt. % or less, copper of 0.45 wt. % to 0.60 wt. %, manganese (Mn) of 0.1 wt. % to 0.20 wt. %, magnesium (Mg) of 1.3 wt. % to 1.5 wt. %, chromium (Cr) of 0.1 wt. % or less, zinc of 4.5 wt. % to 5.1 wt. %, titanium (Ti) of 0.04 wt. % or less, zirconium (Zr) of 0.08 wt. % to 0.12 wt. %, and inevitable impurities of 0.15 wt. % or less.
 2. A method for manufacturing an aluminum alloy material for a bumper beam, comprising: casting into a billet an aluminum alloy which comprises aluminum as a principal element, silicon (Si) of 0.1 wt. % or less, ferrum (Fe) of 0.2 wt. % or less, copper of 0.45 wt. % to 0.60 wt. %, manganese (Mn) of 0.1 wt. % to 0.20 wt. %, magnesium (Mg) of 1.3 wt. % to 1.5 wt. %, chromium (Cr) of 0.1 wt. % or less, zinc of 4.5 wt. % to 5.1 wt. %, titanium (Ti) of 0.04 wt. % or less, zirconium (Zr) of 0.08 wt. % to 0.12 wt. %, and inevitable impurities of 0.15 wt. % or less; extruding the billet into a predetermined form to form an extrusion; performing a solid-solutionization process to quench the extrusion; subjecting the extrusion to an artificial age-hardening which is performed at a temperature of about 120° C. for 24 hours; and subjecting the extrusion an over age-hardening which is performed at a temperature of about 170° C. to 185° C. for 1 hour to 3 hours. 